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Calcium‐binding and temperature induced transitions in equine lysozyme: New insights from the pCa–temperature “phase diagrams”
Author(s) -
Permyakov Sergei E.,
Khokhlova Tatyana I.,
Nazipova Aliya A.,
Zhadan Andrey P.,
MorozovaRoche Ludmila A.,
Permyakov Eugene A.
Publication year - 2006
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.21159
Subject(s) - lysozyme , phase diagram , chemistry , crystallography , phase transition , circular dichroism , phase (matter) , thermodynamics , molten globule , physics , biochemistry , organic chemistry
The most universal approach to the studies of metal binding properties of single‐site metal binding proteins, i.e., construction of a “phase diagram” in coordinates of free metal ion concentration–temperature, has been applied to equine lysozyme (EQL). EQL has one relatively strong calcium binding site and shows two thermal transitions, but only one of them is Ca 2+ ‐dependent. It has been found that the Ca 2+ ‐dependent behavior of the low temperature thermal transition ( I ) of EQL can be adequately described based upon the simplest four‐states scheme of metal‐ and temperature‐induced structural changes in a protein. All thermodynamic parameters of this scheme were determined experimentally and used for construction of the EQL phase diagram in the pCa–temperature space. Comparison of the phase diagram with that for α‐lactalbumin (α‐LA), a close homologue of lysozyme, allows visualization of the differences in thermodynamic behavior of the two proteins. The thermal stability of apo‐EQL (transition I) closely resembles that for apo‐α‐LA (mid‐temperature 25°C), while the thermal stabilities of their Ca 2+ ‐bound forms are almost indistinguishable. The native state of EQL has three orders of magnitude lower affinity for Ca 2+ in comparison with α‐LA while its thermally unfolded state (after the I transition) has about one order lower ( K = 15 M −1 ) affinity for calcium. Circular dichroism studies of the apo‐lysozyme state after the first thermal transition show that it shares common features with the molten globule state of α‐LA. Proteins 2006. © 2006 Wiley–Liss, Inc.